The present invention relates to peptides having neutrophil stimulating activity, and to use of these peptides as therapeutic agents.
Tumour necrosis factor (TNF) was first identified as a factor found in the serum of Bacillus Calmette-Guerin treated mice which caused haemorrhagic regression of certain transplanted tumours and had cytolytic activity on several transformed cell lines in vitro (Carswell et al, PNAS 72, 3666-3670; Helson et al, 1975, Nature 258, 731-732). TNF, a product of activated macrophages, has subsequently been shown to be a primary mediator in the pathology of endotoxic shock (Tracey et al 1986, Science 234, 470-474). In addition to its pathological effects TNF also has a central role in host defences against viral, bacterial and parasitic pathogens.
The cellular targets of TNF important in host defence include neutrophils, eosinophils, monocyte/macrophages and lymphocytes. Within this context TNF is a major mediator of neutrophil activation. TNF stimulates enhanced phagocytosis (Shalaby et al 1985, J.Immunol., 135, 2069-2073), enhanced production of superoxide anions (Teujiimoto et al, 1986, Biochem. Biophys. Res. Commun., 137, 1094-1100), release of lysozyme and hydrogen peroxide and causes neutrophil degranulation (Klebanoff et al, 1986, J.Immunol., 136, 4220-4225). Neutrophils also show enhanced microbiocidal and tumouricidal activity when stimulated by TNF (Shalaby et al, 1985, J.Immunol., 135, 2069-2073; Djeu et al, 1986, J.Immunol., 137, 2980-2984; Blanchard et al, 1989, J.Leuk. Biol., 45, 538-545). It has been hypothesized that the cytostatic effect of TNF is mediated by high local concentrations of hydrogen peroxide produced by neutrophils (Shau 1986, J.Immunol., 141, 234-240).
TNF pretreatment enhances the response of neutrophils to N-formyl-L-methionyl-L-leucyl-L-phenylalanine (F-met-leu-phe) and phorbol myristate acetate through specific receptors (Ferrante et al 1988, Int. Arch. Allergy Appl. Immunol., 86, 82-91). Neutrophils accumulate at sites of inflammation, caused in part by the increased expression of complement receptors by TNF (Berger et al 1988, Blood 71, 151-158). Further TNF causes neutrophil emigration into skin (Cybulsky et al 1988, J. Immunol. 140, 3144-3149).
Neutrophil function is known to be depressed in a number of viral, bacterial and parasitic infections (Abramson and Mills, 1988, Rev. Infect. Dis., 10, 326-341; Ferrante et al, 1989, Immunol. Letts., 22, 301-6). Depressed neutrophil function has, for example, been described in Acquired Immune Deficiency Syndrome (Thorsen et al, 1989, AIDS, 3, 651-653; Ellis et al, 1988, J. Infect. Dis., 158, 1268-1276; Murphy et al, 1988, J. Infect. Dis., 158, 627-630). Clearly TNF, which appears to play an important role in neutrophil activation both in vitro and in vivo as described above, given exogenously has the potential to overcome these neutrophil defects. The administration of TNF or indeed overproduction of TNF is, however, associated with severe side effects and the manifestation of pathology such as thrombocytopaenia, lymphocytopaenia, hepatotoxicity, renal impairment and hypertension.